Advancements in display technology, including the development of plasma display panels (PDPs) and plasma addressed liquid crystal (PALC) displays, have led to an interest in forming electrically-insulating ceramic barrier ribs on glass substrates. The ceramic barrier ribs separate cells in which an inert gas can be excited by an electric field applied between opposing electrodes. The gas discharge emits ultraviolet (uv) radiation within the cell. In the case of PDPs, the interior of the cell is coated with a phosphor that gives off red, green, or blue visible light when excited by uv radiation. The size of the cells determines the size of the picture elements (pixels) in the display. PDPs and PALC displays can be used, for example, as the displays for high definition televisions (HDTV) or other digital electronic display devices.
One way in which ceramic barrier ribs can be formed on glass substrates is by direct molding, which involves laminating a planar rigid mold onto a substrate with a glass- or ceramic-forming composition disposed therebetween. The glass- or ceramic-forming composition is then solidified and the mold is removed. Finally, the barrier ribs are fused or sintered by firing at a temperature of about 550° C. to about 1600° C. The glass- or ceramic-forming composition has micrometer-sized particles of glass frit dispersed in an organic binder. The use of an organic binder allows barrier ribs to be solidified in a green state so that firing fuses the glass particles in position on the substrate. However, in applications such as PDP substrates, highly precise and uniform barrier ribs with few or no defects or fractures are required. These requirements can pose challenges, especially during removal of the rigid mold from the green state ribs.
PDP ribs are typically arranged in one of two pattern types. One type is referred to as a “straight pattern.” This straight pattern is simple and can be relatively easily manufactured on a large scale.
A flexible resin mold can be used to mold ribs having the straight pattern. The resin mold is manufactured in the following way. First, a photosensitive resin is filled into a metal master mold having the same pattern and the same shape as those of the rib pattern to be manufactured. Next, this photosensitive resin is covered with a plastic film and is cured to integrate the photosensitive resin after curing with the film. The film is then released with the photosensitive resin from the metal master mold to form a flexible resin mold.
Another rib pattern type is referred to as a “lattice pattern.” The lattice pattern can be used to improve the vertical resolution of a PDP compared to the straight pattern, because ultraviolet rays from the discharge display cell are better confined and are hence less likely to leak to adjacent cells. In addition, the phosphors can be applied to a relatively greater area of the discharge display cell when lattice pattern ribs are employed.
Methods have previously been described that enable molding and formation of ceramic microstructures such as straight or lattice rib patterns on a patterned substrate. For example, U.S. Pat. No. 6,247,986 B1 to Chiu et al., entitled METHOD FOR PRECISE MOLDING AND ALIGNMENT OF STRUCTURES ON A SUBSTRATE USING A STRETCHABLE MOLD, and U.S. Patent Publication No. 2003/0098528 A1 to Chiu et al., entitled METHOD OF FORMING MICROSTRUCTURES ON A SUBSTRATE USING A MOLD, describe the molding and aligning of ceramic barrier rib microstructures on an electrode-patterned substrate. Such ceramic barrier rib microstructures may be particularly useful in electronic displays, such as PDPs and PALC displays, in which pixels are addressed or illuminated via plasma generation between opposing substrates.
Although a mold can be used to manufacture ribs having the lattice pattern, the removal of a rigid mold typically results in damage to the ribs. A flexible mold as described herein can be applied to molding lattice pattern ribs so that damage to the ribs may be avoided. According to existing molding technology, however, it is difficult to manufacture a mold that eliminates the problem of rib damage upon mold removal. In addition to problems with rib damage upon de-molding, it is preferred not to entrap air bubbles within the mold. Large air bubbles can result in defects large enough to effectively interrupt the continuity of the ribs. Small air bubbles are not as disruptive, but their presence is not preferred.
For the lattice pattern, damage to the lateral ribs (those lying perpendicular to the axis of removal of the flexible mold) is a problem. In addition, the rib material needs to have a sufficiently high viscosity such that it maintains the rib shape after removal of the mold. However, since high viscosity material has low flowability, air bubbles in lateral grooves of the mold are difficult to eliminate completely.